Organopolysilozane compositions crosslinkable with elimination of alcohols to give elastomer

Abstract

Alkoxy RTV-1 compositions comprise the product of the reaction of(A) an HO-terminated organopolysiloxane,(B1) an alkoxysilane which has at least three alkoxy groups and / or its partial hydrolysates, and(B2) an alkoxysilane which has two alkoxy groups and / or its partial hydrolysates, in the presence of(C) an acid phosphoric ester of the general formula (I)wherea is 1 or 2,R1 and R2 are a hydrogen radical, methyl radical or hydroxyl radical,b and d are 2 or 3,c is an integer from 2 to 15,e is 0 or 1L comprises a radical -O-, -COO-, -OOC-, -CONR3-, -NR4CO- or -CO-,R3 and R4 are a hydrogen radical or C1-C10-alkyl radical, andM is a monovalent, unsubstituted or hydroxyl-, fluorine-, chlorine-, bromine-,C1-C10-alkoxyalkyl- or cyano-substituted C1-C20-hydrocarbon radical, with the proviso that on any given carbon atom not more than one radical R1 and R2 may be a hydroxyl radical.

Description

The invention relates to alkoxy RTV-1 compositions which give low-modulus vulcanizates, to the preparation of these compositions, and to their use as sealing compounds for filling joints in natural stone.Unplasticized RTV-1 (room temperature vulcanizable, one part) compositions have unsatisfactory stress-strain behavior for use as permanently flexible sealing materials, since the stress values at, for example, 100% strain ("modulus at 100% strain") are too high. A high 100% modulus (e.g. 0.6 N / mm.sup.2) is associated with a marked increase in stress in the event of widening of the joint, caused for example by changes in temperature, which markedly increases the danger of adhesion failure, i.e. detachment of the flexible sealing material from the respective joint substrate. It has been found in practice, that a 100% modulus of from 0.2 to 0.4 N / mm.sup.2 is desirable for this type of joint.The stress-strain behavior of a silicone rubber vulcanizate is a function of the type and amount...

AI Technical Summary

Benefits of technology

An object of the invention is to provide a simple way of manufacturing alkoxy RTV-1 compositions which are easy to use and which, without adding plasticizer, can be adjusted to have a low modulus. For the purposes of the present invention, the term organopolysiloxanes is intended to include dimeric, oligomeric and polymeric siloxanes.

Another advantage of this process is that no side-reactions occur and, for example, no formation of T units or Q units is observed on linear HO-terminated organopolysiloxanes (A). The acid phosphoric esters (C) do not have to be deactivated immediately after the reaction.

Problems solved by technology

Unplasticized RTV-1 (room temperature vulcanizable, one part) compositions have unsatisfactory stress-strain behavior for use as permanently flexible sealing materials, since the stress values at, for example, 100% strain ("modulus at 100% strain") are too high.

A high 100% modulus (e.g. 0.6 N / mm.sup.2) is associated with a marked increase in stress in the event of widening of the joint, caused for example by changes in temperature, which markedly increases the danger of adhesion failure, i.e. detachment of the flexible sealing material from the respective joint substrate.

However, the use of very long-chain polymers compromises the consistency of the RTV-1 system.

Thus, if the consistency of the filled paste is to be soft and paste-like but also self-supporting, the viscosity of the organopolysiloxane cannot be too high, otherwise the result is a stiff, putty-like paste which is difficult to use.

The fundamental disadvantage of a plasticizer is that it is not chemically bound to the vulcanizate network.

This phenomenon becomes particularly noticeable with joints in porous natural stone, such as marble, granite or altoquartzite, since the periphery of the joint becomes hydrophobicized and darkens therefore permanently, and this is of course undesirable.

However, this process requires an excessive number of operations and gives unvulcanized compositions which are undesirably stiff.

The disadvantages of such preparation need not be stated.